Abstract Detail

Peperomia leaf crystal macropatterns and phylogeny: what can be learned from these two diverse approaches.

Species of the large, basal, pantropical genus Peperomia display leaves that vary widely in shape, thickness, lamina size, and coloration. Internally leaves contain one or two of three forms of calcium oxalate crystals located in palisade cells and spongy parenchyma. Collectively, these crystals form distinct macropatterns in each species. 45 of 48 species comprising a recently published phylogram, based on chloroplast gene profiles, were studied to determine if leaf macropatterns matched the molecular data. Microscopic data, from living and herbarium specimens, showed seven crystal macropatterns were evident from leaf clearings. Druses (spherical crystal aggregates) occur only in palisade cells whereas, when present, raphide (needle-like) bundles or single prisms occur only in spongy mesophyll. All but one species display druses either singly in all palisade cells forming a uniform crystal layer (84%, Uniform) or they occur singly in cells only above veins forming a reticulate pattern (16%; Reticulate). Most species (75%) do not display any crystals in the spongy parenchyma (-raphide bundles/-prisms); however, some clades specifically show spongy parenchyma raphide bundles (16%; +/-) while others have spongy parenchyma prisms (11%; -/+). Several clades display more than one macropattern. A summary of these seven macropatterns included in the phylogram and their percentages are designated as: U-/- (47%), U-/+ (9%) U+/- (7%), UunderVeins+/- (9%), UbigV/smA-/- (9%), R-/- (15%), and R-/+ (2%). Based only on crystal macropatterns, these data do not clearly demonstrate any general trend, and seemingly fail as synapomorphies for most of the clades in Peperomia. However, these results indicate that the presence of specific crystal macropatterns may be controlled by other molecular, physiological and/or environmental factors yet to be determined. The Peperomia data will be compared with other plant groups where crystal macropatterns have been studied.